<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
</head>
<body>
  <!-- label都有哪些作用？并举相应的例子说明  a 标签的 target 属性一共有四个值。 -->
  <input type="checkbox" id="a" value="haha" name="cn">
  <label for="a" >haha </label>
  <input type="checkbox" id="b" value="hehe" name="cm">
  <label for="b" >hehe </label>

  <label for="username" accesskey＝"N">姓名</label><input id="username" type="text">
</body>
</html>